The present invention relates to the field of integrated circuits and in particular, to a programmable slew rate control for a differential output of the integrated circuit.
Integrated circuits are important building blocks of the modern age. Technology continues to evolve and integrated circuits continue to provide improved functionality. As integrated circuits improve, so do the electronics systems that are built using integrated circuits. There are many types of integrated circuit such as memories, micro-processors, application specific integrated circuits (ASICs), and programmable logic. Programmable logic integrated circuits such as PALS, PLDS, FPGAS, LCAS, and others are becoming more complex and continually evolving to provide more user-programmable features on a single integrated circuit.
Data is input and output from integrated circuits. Integrated circuits are used in a wide range of applications, some requiring higher performance than other applications. When higher performance is needed, then integrated circuits should output data in order to meet the performance specification. However, when less performance is sufficient, it is desirable that the output of the integrated circuit can be slowed down.
One of the problems that is important to address when using integrated circuits is noise. Integrated circuits generate noise on a printed circuit board when their outputs switch. Noise is undesirable because if the noise is sufficiently great, it may cause incorrect logic to be input or improper clocking of the integrated circuit or other integrated circuits on the printed circuit board. The amount of noise depends on a number of factors including the edge rate of the output signals. Sharper or faster edge rates tend to generate more noise, while slower slew rate signals have less noise. To address noise, printed circuit boards can be designed to handle noise, but generally at greater expense.
Therefore, it is desirable that differential output drivers of an integrated circuit can be programmably controlled to have a slower slew rate, to reduce noise, especially in those situations where high-speed is not needed.